How to defend against asteroids and meteors

Typically the preserve of science-fiction, now top of the news agenda, the prospect of an asteroid striking earth is raising alarm. This morning a meteor streaked across the sky in Russia, causing explosions and injuring 400 people. Later today a 150-ft asteroid will shave past earth at 17,000 miles distance, the closest recorded. If it hit, it could flatten London. So what defences do we have? Meteors and asteroids have crashed into earth and will do so again. In 1908, one flattened 800 miles of Siberian tundra. Astronomers predict an asteroid spotted in 2004, known as Apophis, will crash in to the earth in 2036.

Even if Apophis misses, Wired report that "it's just a matter of time" before a rock lands plum on planet earth.